Q.
From Dave in Cedar Rapids, Iowa: What causes
the slick coating found on rocks and other solid objects in most streams?

A.
This slippery coating is caused by the secretions of the literally
billions of single-celled algae called diatoms found wherever there
is adequate light and nutrients. The technical name for this
community, including the associated protozoans, bacteria, fungi,
and detritus, is periphyton. This
community is one of the two major food bases for aquatic organisms (the
other is fine particulate organic matter) and is the primary contributor
to dissolved oxygen in the water. Each cell is composed of two pure
silica (glass) halves which fit together like a pill-box. The patterns
of these cases are marked by various striations and patterns, and are
quite beautiful when viewed under a microscope. They are the river
and stream equivalent of phytoplankton, the so-called
"grasses of the sea." ~ Stream Doctor

The 'Stream Doctor' is a retired professional stream ecologist and
author, now living in the West and spending way too much time
fly-fishing. You are invited to submit questions relating to
stream-ecology directly to him for use in this Q & A Feature
at streamdoctor@aol.com.
Please include your name and town.

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